Make --site-per-process override --process-per-tab in RFHM::ShouldTransitionCrossSite

content/browser/frame_host/render_frame_host_manager.cc

Index: content/browser/frame_host/render_frame_host_manager.cc
diff --git a/content/browser/frame_host/render_frame_host_manager.cc b/content/browser/frame_host/render_frame_host_manager.cc
index 4a9034b51560718045abcf988cde7a79027070ab..d8567151a34edf56d27a15e024aa4419c36aa70d 100644
--- a/content/browser/frame_host/render_frame_host_manager.cc
+++ b/content/browser/frame_host/render_frame_host_manager.cc
@@ -844,6 +844,12 @@ bool RenderFrameHostManager::ResetProxiesInSiteInstance(int32 site_instance_id,
 }
 
 bool RenderFrameHostManager::ShouldTransitionCrossSite() {
+  // True for --site-per-process, which overrides both kSingleProcess and
+  // kProcessPerTab.
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kSitePerProcess))
+    return true;
+
   // False in the single-process mode, as it makes RVHs to accumulate
   // in swapped_out_hosts_.
   // True if we are using process-per-site-instance (default) or